Radio Resource (RR) management procedures typically include functions related to the management of the common transmission resources, e.g. the physical channels and the data link connections on control channels.
The purpose of Radio Resource procedures is normally to establish, maintain and/or release RR connections that allow a dialogue between the network and a mobile station (MS), or generally user equipment. This may include cell selection/reselection and handover procedures.
System information and similar information of different types are transmitted by the network on one or more control channels, normally regularly broadcast on the BCCH (Broadcast Control Channel). Based on this information the mobile station is able to decide whether and how it may gain access to the system via the current cell and to cells served by other Radio Access Technologies (RATs).
The Fast Acquisition of System Information procedure was introduced in 3GPP (3rd Generation Partnership Project) Release 8 with the intention of speeding up cell reselection based mobility for a multi-RAT (Radio Access Technology) capable mobile station, e.g. from GERAN (GSM/EDGE Radio Access Network) to UTRAN (Universal Terrestrial Radio Access Network) and/or from GERAN to E-UTRAN (Evolved Universal Terrestrial Radio Access Network).
FIG. 1 is a schematic diagram illustrating an example of mobility between two different RATs, here exemplified by GERAN and UTRAN. The GERAN network 20 normally comprises one or more BSCs (Base Station Controllers) 22 and one or more BTSs (Base Transceiver Stations) 24-1 and 24-2. The UTRAN network 30 normally comprises one or more RNCs (Radio Network Controllers) 32 and one or more NodeBs 34-1 and 34-2. The different Radio Access Technologies (RATs) may have overlapping radio coverage areas. Mobile Stations (MSs) 10 can have multi-RAT capabilities that enable mobility between the different RATs. The mobility is among others based on the input parameters broadcasted by the Radio Access Network (RAN), e.g. in GERAN in the System Information (SI) messages. In this example, the BSC 22 assembles the System Information message and after the assembly the SI message is transferred over the Abis link from the BSC 22 to the BTS 24-1. The BTS 24-1 normally transmits the SI message on the Broadcast Common Control Channel (BCCH) over the Um interface (GERAN radio interface). Mobile Stations 10 then acquire the SI message and apply it e.g. for inter-RAT cell re-selection to UTRAN.
In general, there may be a first radio access network of a first RAT and a second radio access network of a second different RAT, where a mobile station connected to the first radio access network needs to acquire information related to the second radio access network for enabling mobility to the second radio access network.
One specific example of a System Information message is the SI2quater message, as defined in 3GPP TS 44.018 section 9.1.34a ref [1]. In order to speed up cell reselection based mobility to another RAT, a multi RAT capable Mobile Station (MS) does not have to read all message instances of the SI2quater message. This is defined as the Fast Acquisition of System Information procedure and is defined in 3GPP TS 44.018 section 3.4.1.2.1.11, ref [1]. This procedure is to be applied by a multi RAT capable MS for UTRAN if the 3G Priority Parameters Description IE is present in the SI2quater message or 3G Supplementary Parameters Description IE is present in the MEASUREMENT INFORMATION message (ref [1]) or for E-UTRAN if the E-UTRAN Parameters Description IE is present in the SI2quater or MEASUREMENT INFORMATION messages.
From here on the SI2quater message is primarily discussed, however the same problems and the same proposed measures are also valid for the MEASUREMENT INFORMATION message and other similar information messages. The SI2quater message is generally denoted as a System Information message broadcasted to all mobile stations in idle mode camping in the cell while the MEASUREMENT INFORMATION message is a dedicated message sent on the Slow Associated Control Channel (SACCH) to a single MS.
In the definition of the Fast Acquisition of SI procedure, e.g. reference can be made to section 3.4.1.2.1.11 in 3GPP TS 44.018, ref [1], it is stated that the network shall ensure that UTRAN (respectively E-UTRAN) neighbour cell list, measurement parameters and possible priority information (priority information only provided in SI2quater message, i.e. not in MEASUREMENT INFORMATION message) are contained in consecutive instances of the SI2quater message together forming a UTRAN Information Set (respectively E-UTRAN Information Set). The first SI2quater message instance containing UTRAN (respectively E-UTRAN) neighbour cell list and/or measurement parameters and/or priority information shall contain a start bit, UTRAN_Start (respectively E-UTRAN_Start), indicating the start of the UTRAN Information Set (respectively E-UTRAN Information Set), while the last SI2quater message instance containing UTRAN (respectively E-UTRAN) neighbour cell list and/or measurement parameters and/or priority information shall contain a stop bit, UTRAN_Stop (respectively E-UTRAN_Stop), indicating the end of the UTRAN Information Set (respectively E-UTRAN Information Set).
By way of example, for UTRAN related information the UTRAN neighbour cell list and UTRAN measurement parameters are contained within two 3GPP pre-Release 5 structures (3G Neighbour Cell Description struct and 3G Measurement Parameters Description struct) in the SI2quater message while the UTRAN_Start and UTRAN_Stop bits are contained in the 3G Priority Parameters Description IE which is part of a 3GPP Release-8 extension in the SI2quater message.
To be able to build the SI2quater message and the UTRAN Information Set according to the procedural text in 3GPP TS 44.018 section 3.4.1.2.1.11, the network has to include the UTRAN_Start bit in the first instance of the SI2quater message containing UTRAN related information (i.e. UTRAN neighbour cell list and UTRAN measurement parameters) and the UTRAN_Stop bit in the last instance of the SI2quater message containing UTRAN related information (e.g. UTRAN priority information).
Presuming the network starts building the SI2quater message by including all pre-Release 5 related information including the complete (or part of) UTRAN Neighbour Cell list in the first instance of the message, this message instance also has to contain the Release-8 extension part in which the UTRAN_Start bit is set to “1” and the UTRAN_Stop bit is set to “0”.
To be able to include this single bit of information (UTRAN_Start bit=1) in the first instance of the SI2quater message containing UTRAN related information (3G Neighbour Cell Description IE and 3G Measurement Parameters Description IE), the message has to include a number of overhead related bits preceding and following the UTRAN_Start bit. If e.g. starting from the Release 5 extension bit, this non-informative part of the message instance consists of 18 bits of Concrete Syntax Notification 1 (CSN.1) overhead as exemplified in the enclosed Table 1 (highlighted) included in Appendix 1. CSN.1 is a message encoding format used in the GERAN specifications. Please observe that only a part of the SI2quater message (SI2quater Rest Octets IE) is shown in the table.
Considering one instance of the SI2quater message may carry a maximum of 20 octets (see 3GPP TS 44.018 section 10.5.2.33b) of information, a “waste” of 2 octets as in the example above is really remarkable. This particular problem analysis with regard to the SI2quater message is in no way limiting the scope of the proposed technology, as readily understood by the skilled person.
There is in fact a general demand for more efficient mechanisms for supporting and performing acquisition of an information set for enabling mobility to another radio access network of a different radio access technology.